CD28 is required for optimal induction, but not maintenance, of vaccine-induced immunity to Blastomyces dermatitidis.

Cellular immunity mediated by T lymphocytes, in particular CD4+ and CD8+ type 1 cells, is the main defense against pathogenic fungi. Here, CD28-deficient (CD28-/-) mice were used to study the role of costimulation for the generation and maintenance of T-cell-mediated, type 1 cytokine-dependent mechanisms of vaccine immunity to Blastomyces dermatitidis infection. Disruption of CD28 costimulation reduced the number of type 1 CD4 and CD8 cells generated and impaired resistance to infection. Type 1 T-cell subsets generated in vaccinated CD28-/- mice were durable and protected mice for at least 3 months after vaccination. Our findings suggest that CD28 is required for the induction of optimal, protective T-cell responses to B. dermatitidis infection but may be dispensable for the maintenance of T-cell memory.